Chemical Properties of Amino Acids

The chemical properties of amino acids are generally those of the amino group and the carboxyl group, although some other properties which are due to the presence of amino and carboxyl groups in the same molecule are also responded by the amino acids.

Reactions of Amino Group

Reaction with Mineral Acids

Amino acids forms salts with mineral acids which are sparingly soluble in water.

Alkylation of Amino Acids

Amino acids in alkaline solution react with alkyl halides to form N-alkylsubstituted amino acids.

When large excess of alkyl halides is used, internal quarternary alkylammonium salts are formed. These salts have zwitterionic character and are known as betaines.
NH₃⁺–CH₂–COO⁻ + 3CH₃I → (CH₃)₃N⁺–CH₂–COO⁻

Acylation of Amino Acids

The amino group may be acylated by acid chlorides or anhydride.

Reaction with Nitrous Acid

α- amino acids react with nitrous acid to give α- hydroxy acids and nitrogen.

Reaction with Nitrosyl Chloride or Bromide

Amino acids react with nitrosyl halides to form the corresponding halogen acids.

Deamination of Amino Acids

Amino acids on heating with hydroidic acid (HI) at 200° C gives the corresponding fatty acids with the elimination of ammonia.

Reactions of Carboxyl Group

Reaction with Alkalies

Amino acids form salts with alkalies.

NH₂–CH₂–COOH + NaOH → NH₂–CH₂–COONa + H₂O

Esterification of Amino Acids

Amino acids form salts with alkalies.

Decarboxylation of Amino Acids

Amino acids lose carbon dioxide and yield primary amines when heated with barium hydroxide solution.
NH₂–CH₂–COOH + Ba(OH)₂ → CH₃–NH₂ + Ba(CO)₃ + H₂O

Reduction of Amino Acids

Amino acids undergo reduction with LiAlH₄ to form amino alcohols.

Reactions Involving both the Carboxyl and Amino Groups

Action of Heat of Amino Acids

The action of heat on amino-acids is a useful property for distinguishing the different types of amino-acids (viz. α, β, γ and δ); since, the different amino-acids forms different products on heating. Click for Reactions

Reaction with Isocyanates (Formation of Hydantoin)

α- amino acids reacts with isocyantaes to form the corresponding carbamides which on warming with HCl produce hydantoin which is used in the synthesis of other amino acids.

Formation of Sydnone

N-alkyl or aryl amino acids gives N-nitroso derivatives with nitrous acid which on dehydration gives sydnone.

Reaction with Ninhydrine

All α-amino acids react with ninhydrine to produce the same purple complex. This reaction is commonly used to test the presence of α-amino acids.